The addition of a composition such as a gel containing glyceryl trintrate (GTN) as vasodilator, as disclosed in WO02/078580, to the inside of the closed end of a condom is of significant benefit to those men who suffer a partial or complete loss of erection due to the reduction of sensation when using a condom. GTN is readily absorbed through the glans penis. Once absorbed, it acts as a vasodilator, promoting blood flow into the penis and so helping such men to maintain a full erection during intercourse when wearing a condom.
A disadvantage of the invention described in WO02/078580 is that GTN is unstable and degrades in contact with natural rubber latex condoms and also condoms made from synthetic rubber latices such as polyisoprene. This instability significantly limits the shelf life of condoms containing compositions including GTN.
It is known from Chimia, 58 (2004), 401-408 (Chemical Stability, Compatibility and Shelf Life of Explosives) that the decomposition (ageing) reactions of aliphatic nitrate ester explosives such as GTN can be suppressed by the use of aromatic amines or urea derivatives as stabilisers. Aromatic amines and urea derivatives are basic, from which the skilled person seeking to stabilise GTN in condoms would consider using an alkaline or basic substance. Further, this paper discloses that the radicals and acids present in the reaction mixture auto-catalyse some of the decomposition reactions. This paper also states that the decomposition reactions are catalysed by moisture and residual acids, or by water and acids formed during decomposition. Again, this indicates that decomposition is auto-catalytic under acid conditions. Based on this information, a skilled person would not consider using an acidic substance if he was looking to increase the stability of GTN.